User's Manual

R01UH0823EJ0110 Rev.1.10 Page 317 of 1852
Nov 30, 2020
RX23W Group 16. Buses
Figure 16.2 Priority Order between Internal Peripheral Bus Accesses
16.2.5 Write Buffer Function (Internal Peripheral Bus)
The internal peripheral bus has the write buffer function, which allows the next round of bus access to start, before the
current write access is completed, in write access. However, if the following round of bus access is from the same bus
master but to the different internal peripheral bus, it is suspended until the bus operations already in progress are
completed. When read access to the internal memory is scheduled after the write access to the internal peripheral bus
from the CPU, the following round of bus access can be started before the current bus operation is completed and thus
the order of accesses may be changed (Refer to Figure 16.3).
Figure 16.3 Write Buffer Function
Internal main bus 2
(R11) R12
R24 R25R21
Internal main bus 1
(R11)
R22 R23
(R11) R11
Internal main bus 2
(R11) R13
R25R23 R24R21
Internal main bus 1
R11
(R22) R22
(R12)
>
R12
>
(R13) (R13) R13
Request issued; not accepted
Request issued; accepted
No request issued
Priority order fixed:
Priority order toggled:
(1) (2)
(*)
*
(1), (2) : The priority order does not change because the priority of the accepted request is low.
> > > > > > >
> > > >
> > >
Internal peripheral bus 2
Internal peripheral bus 1
Memory bus 1 RAMRAM
Write access to peripheral bus 1
Access by the CPU:
(1) Peripheral bus 1 (W) → (2) Peripheral bus 1 (W) → (3) Peripheral bus 2 (W) → (4) Peripheral bus 2 (W) →
(5) RAM (R) → (6) RAM (R)
Number of access cycles: 1 cycle (peripheral bus 1), 2 cycles (peripheral bus 2)
(1) (2)
(5) (6)
(3) (4)
Write access to peripheral bus 2
Read access to
RAM
Peripheral bus 2 Peripheral bus 2
Peripheral
bus 1
Peripheral
bus 1